CD5 and CD23 Positive Mantle Cell Lymphoma Detected by Flow Cytometry and Confirmed by FISH Study t(11;14).

The differential diagnoses of CD5 positive B-cell lymphoproliferative disorders mainly include chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) and mantle cell lymphoma. Occasionally large cell and marginal zone lymphomas may also be CD5 positive. An accurate diagnosis effects patient management.

The classical immunophenotype for chronic lymphocytic leukemia/small lymphocytic lymphoma is CD19/CD5/CD23 positive FMC-7 negative cells with dim CD20 and dim light chain expressions, while mantle cell lymphoma is CD19/CD5/FMC-7 positive with bright CD20 and bright light chain expressions. The diagnosis of mantle cell lymphoma is usually confirmed by either immunostain for cyclin D1 or FISH study for t(11;14). In reality, immunostaining for cyclin D1 can be difficult and may show variable results in different laboratories and FISH study may not be readily available. Generally, when it comes to the diagnosis of lymphoma, immunohistochemical positivity of both CD5 and CD23 is almost pathognomic for chronic lymphocytic leukemia/small lymphocytic lymphoma if no fresh tissue is saved for flow cytometry analysis.

Flow cytometry analysis of 44 FISH-confirmed mantle cell lymphomas was reviewed in our lab. Among these, 37 showed the classical immunophenotype of mantle cell lymphoma. However, 7 cases (16%) were positive for both CD5 and CD23. The expression of CD23 varied from dim to bright. When compared to typical CLL, they showed FMC-7 expression and brighter than dim light chain expression. In one case, the light chain expression was dim.

In conclusion, CD23 expression which was thought to be a specific marker for CLL/SLL may also be seen with mantle cell lymphoma. Although FMC-7 expression is seen in all CD23 positive mantle cell lymphomas, bright light chain expression is not universal. We recommend that FISH or immunohistochemical studies for cyclin D1 be performed on CD5/CD19 clonal B cell proliferations with CD23 expression if morphology or immunophenotype is atypical for CLL/SLL.